Flash Flood Guidance
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Issued by NWS
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158 AWUS01 KWNH 141252 FFGMPD MOZ000-ARZ000-141830- Mesoscale Precipitation Discussion 0881 NWS Weather Prediction Center College Park MD 851 AM EDT Wed Aug 14 2024 Areas affected...Northwest/North-central MO to North-central/Northeast AR... Concerning...Heavy rainfall...Flash flooding likely Valid 141250Z - 141830Z SUMMARY...A pair of mature warm advection induced MCSs are likely to continue and merge over the next few hours. Reducing convergence should help to reduce coverage and intensity of rainfall but a swath of 2-4" due to training may still pose possible localized flash flooding through early afternoon. DISCUSSION...GOES-E 10.3um shows a slowly decaying MCC with increasingly more isolated overshooting tops to -80C across NE to north-central MO with impressive outflow feathering of cirrus along nearly all quadrants of the complex indicative of the continued solid outflow and maintenance of the complex as it rolls southeastward along the 500-1000 thickness gradient. Downstream, a more linear warm advection complex remains across south-central MO into north-central and northeast AR. Very cold tops with the upstream edge continuing to develop/cool maintains solid potential for heavy rainfall rates and training for flash flooding. While diurnal weakening of the MCSs is to be expected due to slacking LLJ, current VWP trends are maintaining at 25-30kts of 850mb flow perpendicular to the frontal zone still supporting solid insentropic ascent and moisture convergence. Veering with height even by 700mb shows steering remains NNW to SSE becoming more due south into AR, at the northeast edge of the synoptic ridge over TX/OK. This helps to concentrate enhanced moisture up to 2.25" while also supporting a steering flow mainly parallel to the ascent/convergence axis. MUCAPE remains sufficient at 1500-2000 J/kg along the western edge of the complexes. So rainfall efficiency will remain solid in the 2-2.5"/hr range. The upstream MCC had generated a stronger cold pool and stronger mid-level `dry-slot` jet that is mixing some increased momentum air downward to advance southward propagation a bit faster. WAA along/ahead of the wave will help to fill in convective line through central MO, but the upstream convective line will surge southward effectively collecting the training axis across south-central MO as long as the LLJ winds do not diminish too much too quickly. As such, an axis of 2-4" totals can be expected across central to south-central MO and likely intersect areas already experiencing flash flooding conditions as noted by MRMS Flash with 200-600 cfs/smi. As such, flash flooding is likely to continue across that area. Further south into northern AR, environmental parameters diverge a bit with deeper layer flow/steering becomes a bit more divergent through depth; moisture axis shifts eastward , while LLJ further veers to more westerly supporting a more westward propagation vector which also aligns with the instability axis further west. This adds to a bit more uncertainty in placement and potential for higher rainfall totals...but still intensity of rainfall over 2" and spots of 3"+ still have solid potential for localized flash flooding conditions through early afternoon as well. Gallina ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...EAX...LSX...LZK...MEG...SGF... ATTN...RFC...ABRFC...LMRFC...MBRFC...NCRFC...NWC... LAT...LON 40109349 39639225 38749149 36599130 35779028 34959032 34669137 35029232 35909296 36689309 37649339 38439381 38849424 39309465 39629478 39999441